Hard disk drives are used in almost all computer system operations. In fact, most computing systems are not operational without some type of hard disk drive to store the most basic computing information such as the boot operation, the operating system, the applications, and the like. In general, the hard disk drive is a device which may or may not be removable, but without which the computing system will generally not operate.
The basic hard disk drive model was established approximately 40 years ago and resembles a phonograph. That is, the hard drive model can include a storage disk or hard disk that spins at a standard rotational speed. A magnetic read/write transducer head can be mounted on an actuator arm for reading/writing information to or from a location on the disk. The actuator arm or slider is utilized to reach out over the disk to or from a location on the disk. The complete assembly, e.g., the arm and head, is called a head gimbal assembly (HGA).
In operation, the hard disk is rotated at a set speed via a spindle motor assembly having a central drive hub. Additionally, there are channels or tracks evenly spaced at known intervals across the disk. When a request for a read of a specific portion or track is received, the hard disk aligns the head, via the arm, over the specific track location and the head reads the information from the disk. In the same manner, when a request for a write of a specific portion or track is received, the hard disk aligns the head, via the arm, over the specific track location and the head writes the information to the disk.
Over the years, refinements of the disk and the head have provided great reductions in the size of the hard disk drive. For example, the original hard disk drive had a disk diameter of 24 inches. Modern hard disk drives are much smaller and include disk diameters of less than 2.5 inches (micro drives are significantly smaller than that). Refinements also include the use of smaller components. That is, by reducing the read/write tolerances of the head portion, the tracks on the disk can be reduced in size by the same margin. Thus, as modern micro recognition technology is applied to the head, the track size on the disk can be further compressed.
A second refinement to the hard disk drive is the reduction of the “flying” height at which the magnetic read/write transducer head operates or flies above the disk. As the flying height has been continually reduced, a greater number of data can be stored on a disk surface. Note that during a disk drive manufacturing process, if the flying height is either too high or too low, the resulting disk drive may not operate properly. As such, it is desirable to be able to measure the flying height accurately. However, as the flying heights have become ever smaller, for example, less than 10 nanometers (nm), it has become more difficult to accurately measure the flying height.
For example, some conventional techniques for attempting to measure the flying height can involve signal measurements using pulse width measurements, amplitude measurements, or third harmonic techniques. However, as flying heights get smaller and smaller and density gets higher and higher, these signal measurement techniques are not as desirable due to head saturation and low third harmonic amplitude. As such, these techniques are not as accurate.